The present invention relates to seals in general, and more particularly to a seal for a plate-shaped closure. Even more particularly, the invention relates to a seal for a plate-shaped closure which is pivotally mounted in a tubular housing.
It is already known, in connection with a plate-shaped closure of the last-mentioned type, to provide an annular, elastic, metallic and lip-shaped sealing element in the housing around the closure, which sealing element then cooperates with a seating surface of the plate-shaped closure, and the arrangement of which renders it possible to achieve a sealing effect in both directions of flow.
Experience has shown that the conventional sealing elements of this type, which, because of the conditions of their use, are required to be made of metallic material, accomplish their sealing function, generally speaking, only in an imperfect manner. In order to obtain a low rate of leakage, the sealing element must be fitted to the circumferential surface of the plate-shaped closure with a high degree of accuracy. It is well known that thin-walled parts of sheet metal can be manufactured with the accuracy required for achieving a low leakage rate only at a high expense. Consequently, high sealing effects can be achieved only with difficulty, if at all, by resorting to the use of such sealing arrangements.
The German published patent application DE-OS No. 25 52 524 discloses a seal which is mounted in a housing and which is supported by pressure in both directions of flow. An important disadvantage of this arrangement is to be seen in the fact that the sealing element must conduct pivotal movements in order to achieve the sealing effect. Now, in order to avoid the pressing-through of this sealing element by the pressure acting thereon, there are provided lateral abutments which limit the extent of pivoting of the sealing element. Once the sealing element abuts the respective abutment, a gap comes into existence between the sealing element and the other abutment. In view of the fact that, for all intents and purposes, the conveyed medium always includes contaminants, there exists the danger that this gap may or will become clogged. When this happens, the reliability of the sealing element can no longer be assured.